HIGH PERFORMANCE AlSiMgCu CASTING ALLOY

ABSTRACT

New aluminum casting alloys having 8.5-9.5 wt. % silicon, 0.8-2.0 wt. % copper (Cu), 0.20-0.53 wt. % magnesium (Mg), and 0.35 to 0.8 wt. % manganese are disclosed. The alloy may be solution heat treated, treated in accordance with T5 tempering and/or artificially aged to produce castings, e.g., for cylinder heads and engine blocks. In one embodiment, the castings are made by high pressure die casting.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority to U.S. Provisional PatentApplication No. 61/919,415, filed Dec. 20, 2013, entitled “HighPerformance AlSiMgCu Casting Alloy with Engine and HPDC Applications”,and International Patent Application No. PCT/US14/70938, filed Dec. 17,2014, entitled “HIGH PERFORMANCE AlSiMgCu CASTING ALLOY”. All of theabove-identified patent applications are incorporated herein byreference in their entirety.

FIELD

The present invention relates to aluminum alloys, and more particularly,to aluminum alloys used for making cast products.

BACKGROUND

Aluminum alloys are widely used, e.g., in the automotive and aerospaceindustries, due to a high performance-to-weight ratio, favorablecorrosion resistance and other factors. Various aluminum alloys havebeen proposed in the past that have characteristic combinations ofproperties in terms of weight, strength, castability, resistance tocorrosion, and cost. AlSiMgCu casting alloys are described incommonly-owned U.S. Patent Application Publication No. 2013/0105045,entitled “High-Performance AlSiMgCu Casting Alloy”, published May 2,2013.

SUMMARY

The disclosed subject matter relates to improved aluminum casting alloys(also known as foundry alloys) and methods for producing same. Morespecifically, the present application relates to new aluminum castingalloys having:

-   -   8.5-9.5 wt. % silicon;    -   0.5-2.0 wt. % copper (Cu);        -   wherein 2.5≦(Cu+10Mg)≦5.8;    -   0.15-0.60 wt. % magnesium (Mg);    -   0.35 to 0.8 wt. % manganese;    -   up to 5.0 wt. % zinc;    -   up to 1.0 wt. % silver;    -   up to 1.0 wt. % nickel;    -   up to 1.0 wt. % hafnium;    -   up to 1.0 wt. % iron;    -   up to 0.30 wt. % titanium;    -   up to 0.30 wt. % zirconium;    -   up to 0.30 wt. % vanadium;    -   up to 0.10 wt. % of one or more of strontium, sodium and        antimony;    -   other elements being ≦0.04 wt. % each and ≦0.12 wt. % in total;    -   the balance being aluminum.        The new aluminum casting alloys may be utilized in a variety of        applications, including engine applications (e.g., as a cylinder        head, as a cylinder/engine block) and automotive applications        (e.g., suspension and structural components, connecting rods),        among others.

I. Composition

As noted above, the new aluminum casting alloys generally include8.5-9.5 wt. % Si. In one embodiment, the aluminum alloy includes8.75-9.5 wt. % Si. In one embodiment, the aluminum alloy includes8.75-9.25 wt. % Si.

As noted above, the new aluminum casting alloys generally include0.5-2.0 wt. % copper (Cu). In one approach, the aluminum alloy includes0.8 to 2.0 wt. % copper. In another approach, the aluminum alloyincludes 1.0 to 1.5 wt. % copper. In yet another approach, the aluminumalloy includes 0.7 to 1.3 wt. % copper. In another approach, thealuminum alloy includes 0.8 to 1.2 wt. % copper.

As noted above, the new aluminum casting alloys generally include0.15-0.60 wt. % Mg. In one approach, the aluminum alloy includes0.20-0.53 wt. % magnesium (Mg). In one approach the alloy includes ≧0.36wt. % magnesium (e.g., 0.36-0.53 wt. % Mg). In one approach, thealuminum alloy includes from 0.40 to 0.45 wt. % magnesium. In anotherapproach, the alloy includes ≦0.35 wt. % magnesium (e.g., 0.15-0.35 wt.% Mg). In one another approach, the alloy includes 0.20-0.25 wt. % Mg.Other combinations of magnesium and copper are described below.

The amount of copper plus magnesium may be limited to ensure anappropriate volume fraction of Q phase, as described below. For productsto be processed to a T5 temper, and having 0.15-0.35 wt. % Mg (e.g.,0.20-0.25 wt. % Mg), a new aluminum casting alloy may include an amountof copper plus magnesium such that 2.5≦(Cu+10Mg)≦4.5. In one embodiment,a new aluminum casting alloy includes an amount of copper plus magnesiumsuch that 2.5≦(Cu+10Mg)≦4.0. In another embodiment, a new aluminumcasting alloy includes an amount of copper plus magnesium such that 2.5≦(Cu+10Mg)≦3.75. In yet another embodiment, a new aluminum casting alloyincludes an amount of copper plus magnesium such that 2.5≦(Cu+10Mg)≦3.5. In another embodiment, a new aluminum casting alloyincludes an amount of copper plus magnesium such that2.5≦(Cu+10Mg)≦3.25. In yet another embodiment, a new aluminum castingalloy includes an amount of copper plus magnesium such that2.75≦(Cu+10Mg)≦3.5. In any of the embodiments of this paragraph themagnesium within the aluminum alloy may be limited to 0.15-0.30 wt. %Mg, such as limited to 0.20-0.25 wt. % Mg.

For products to be processed to any of a T5, T6 or T7 temper, a newaluminum casting alloy includes an amount of copper plus magnesium suchthat 4.7≦(Cu+10Mg)≦5.8. In one embodiment, a new aluminum casting alloyincludes an amount of copper plus magnesium such that 4.7≦(Cu+10Mg)≦5.7.In another embodiment, a new aluminum casting alloy includes an amountof copper plus magnesium such that 4.7≦(Cu+10Mg)≦5.6. In yet anotherembodiment, a new aluminum casting alloy includes an amount of copperplus magnesium such that 4.7≦(Cu+10Mg)≦5.5. In yet another embodiment, anew aluminum casting alloy includes an amount of copper plus magnesiumsuch that 4.8≦(Cu+10Mg)≦5.5. In another embodiment, a new aluminumcasting alloy includes an amount of copper plus magnesium such that4.9≦(Cu+10Mg)≦5.5. In yet another embodiment, a new aluminum castingalloy includes an amount of copper plus magnesium such that5.0≦(Cu+10Mg)≦5.5. In another embodiment, a new aluminum casting alloyincludes an amount of copper plus magnesium such that 5.0≦(Cu+10Mg)≦5.4.In yet another embodiment, a new aluminum casting alloy includes anamount of copper plus magnesium such that 5.1≦(Cu+10Mg)≦5.4. In any ofthe embodiments of this paragraph, the magnesium within the aluminumalloy may be toward the higher end of the acceptable range, such as from0.30-0.60 wt. % Mg, or 0.35-0.55 wt. % Mg, or 0.37-0.50 wt. % Mg. or0.40-0.50 wt. % Mg, or 0.40-0.45 wt. % Mg. In one approach, the aluminumalloy includes about 1.0 wt. % copper (e.g., 0.90-1.10 wt. % Cu, or0.95-1.05 wt. % Cu) in combination with about 0.4 wt. % magnesium(0.35-0.45 wt. % Mg, or 0.37-0.43 wt. % Mg).

As noted above, the new aluminum casting alloys generally include 0.35to 0.8 wt. % manganese. In one approach, the aluminum alloy includes0.45-0.70 wt. % Mn. In another approach, the aluminum alloy includes0.50-0.65 wt. % Mn. In another approach, the aluminum alloy includes0.50-0.60 wt. % Mn. In one approach, the weight ratio of iron tomanganese (Fe:Mn) in the aluminum alloy is ≦0.50. In another approach,the weight ratio of iron to manganese (Fe:Mn) in the aluminum alloy is≦0.45. In another approach, the weight ratio of iron to manganese(Fe:Mn) in the aluminum alloy is ≦0.40. In another approach, the weightratio of iron to manganese (Fe:Mn) in the aluminum alloy is ≦0.35. Inanother approach, the weight ratio of iron to manganese (Fe:Mn) in thealuminum alloy is ≦0.30.

As noted above, the new aluminum casting alloys may include up to 1.0wt. % Fe. In one approach, the aluminum alloy includes from 0.01 to 0.5wt. % Fe. In another approach, the aluminum alloy includes from 0.01 to0.35 wt. % Fe. In yet approach, the aluminum alloy includes from 0.01 to0.30 wt. % Fe. In another approach, the aluminum alloy includes from0.01 to 0.25 wt. % Fe. In yet approach, the aluminum alloy includes from0.01 to 0.20 wt. % Fe. In another approach, the aluminum alloy includesfrom 0.01 to 0.15 wt. % Fe. In yet another approach, the aluminum alloyincludes from 0.10 to 0.30 wt. % Fe.

As noted above, the new aluminum casting alloys may include up to 5.0wt. % Zn. In one approach, the alloy includes ≦0.5 wt. % Zn. In anotherapproach, the aluminum alloy includes ≦0.25 wt. % Zn. In yet anotherapproach, the aluminum alloy includes ≦0.15 wt. % Zn. In anotherapproach, the aluminum alloy includes ≦0.05 wt. % Zn. In yet anotherapproach, the aluminum alloy includes ≦0.01 wt. % Zn.

As noted above, the new aluminum casting alloys may include up to 1.0wt. % Ag. In one embodiment, the aluminum alloy includes ≦0.5 wt. % Ag.In another approach, the aluminum alloy includes ≦0.25 wt. % Ag. In yetanother approach, the aluminum alloy includes ≦0.15 wt. % Ag. In anotherapproach, the aluminum alloy includes ≦0.05 wt. % Ag. In yet anotherapproach, the aluminum alloy includes ≦0.01 wt. % Ag.

As noted above, the new aluminum casting alloys may include up to 1.0wt. % Ni. In one embodiment, the aluminum alloy includes ≦0.5 wt. % Ni.In another approach, the aluminum alloy includes ≦0.25 wt. % Ni. In yetanother approach, the aluminum alloy includes ≦0.15 wt. % Ni. In anotherapproach, the aluminum alloy includes ≦0.05 wt. % Ni. In yet anotherapproach, the aluminum alloy includes ≦0.01 wt. % Ni.

As noted above, the new aluminum casting alloys may include up to 1.0wt. % Hf. In one embodiment, the aluminum alloy includes ≦0.5 wt. % HfIn another approach, the aluminum alloy includes ≦0.25 wt. % Hf In yetanother approach, the aluminum alloy includes ≦0.15 wt. % Hf In anotherapproach, the aluminum alloy includes ≦0.05 wt. % Hf In yet anotherapproach, the aluminum alloy includes ≦0.01 wt. % Hf.

As noted above, the new aluminum casting alloys may include up to 0.30wt. % each of zirconium and vanadium. For high pressure die castingembodiments, both zirconium and vanadium may be present, and in anamount of at least 0.05 wt. % each, and wherein the total amount of Zr+Vdoes not form primary phase particles (e.g., the total amount of Zr+V isfrom 0.10 wt. to 0.50 wt. %). In one embodiment, the aluminum alloyincludes at least 0.07 wt. % each of zirconium and vanadium, and Zr+V isfrom 0.14 to 0.40 wt. %. In one embodiment, the aluminum alloy includesat least 0.08 wt. % each of zirconium and vanadium, and Zr+V is from0.16 to 0.35 wt. %. In one embodiment, the aluminum alloy includes atleast 0.09 wt. % each of zirconium and vanadium, and Zr+V is from 0.18to 0.35 wt. %. In one embodiment, the aluminum alloy includes at least0.09 wt. % each of zirconium and vanadium, and Zr+V is from 0.20 to 0.30wt. %. In another approach, the aluminum alloy includes ≦0.03 wt. % eachof zirconium and vanadium (e.g., as impurities for non-HPDCapplications).

As noted above, the new aluminum casting alloys may include up to 0.30wt. % titanium. In one embodiment, the aluminum alloy includes from0.005 to 0.25 wt. % Ti. In another embodiment, the aluminum alloyincludes from 0.005 to 0.20 wt. % Ti. In yet another embodiment, thealuminum alloy includes from 0.005 to 0.15 wt. % Ti. In anotherembodiment, the aluminum alloy includes from 0.01 to 0.15 wt. % Ti. Inyet another embodiment, the aluminum alloy includes from 0.03 to 0.15wt. % Ti. In another embodiment, the aluminum alloy includes from 0.05to 0.15 wt. % Ti. When both zirconium and titanium are used in the newaluminum alloy, the aluminum alloy generally includes at least 0.005 wt.% Ti, such as any of the amounts of titanium described above. In oneembodiment, the aluminum alloy includes at least 0.09 wt. % each ofzirconium and vanadium, and Zr+V is from 0.18 to 0.35 wt. % and from0.05 to 0.15 wt. % Ti.

As noted above, the new aluminum casting alloys may include up to 0.10wt. % of one or more of strontium, sodium and antimony. In one approach,the aluminum alloy includes ≦0.05 wt. % strontium. In one approach, thealuminum alloy includes ≦0.03 wt. % sodium. In one approach, thealuminum alloy includes ≦0.03 wt. % antimony. In one embodiment, thealuminum alloy includes strontium, and from 50-300 ppm of strontium. Inone embodiment, the aluminum alloy is free of sodium and antimony, andincludes these elements as impurities only.

As noted above, the new aluminum casting alloys generally include otherelements being ≦0.04 wt. % each and ≦0.12 wt. % in total, the balancebeing aluminum. In one embodiment, the new aluminum casting alloysgenerally include other elements being ≦0.03 wt. % each and ≦0.10 wt. %in total, the balance being aluminum

In one embodiment, the new aluminum casting alloy includes 9.14-9.41 wt.% Si, 0.54-1.53 wt. % Cu, 0.21-0.48 wt. % Mg, 0.48-0.53 wt. % Mn,0.13-0.17 wt. % Fe, 0.11-0.30 wt. % Ti, 0.10-0.14 wt. % Zr, 0.12-0.13wt. % V, ≦0.05 wt. % Zn, ≦0.05 wt. % Ag, ≦0.05 wt. % Ni, ≦0.05 wt. % Hf,up to 0.012 wt. % Sr, other elements being ≦0.04 wt. % each and ≦0.12wt. % in total, the balance being aluminum. For alloys to be processedto the T5 temper, this alloy may include 0.20-0.25 wt. % Mg, and withCu+10Mg being from 2.5 to 4.0. For alloys to be processed to any of aT5, T6 or T7 temper, this alloy may include 0.40-0.48 wt. % Mg, and withCu+10Mg being from 4.7 to 5.8.

II. Processing

The new aluminum casting alloy may be shape cast in any suitable form orarticle. In one approach, the new aluminum alloy is shape cast in theform of an automotive component or engine component (e.g., a cylinderhead or cylinder/engine block).

In one approach, a method of producing a shape cast article includes thesteps of:

-   -   (a) obtaining the above-described aluminum alloy by melting the        appropriate amounts of the above-described elements in an        appropriate melting apparatus;    -   (b) introducing the molten aluminum alloy into a mold; and    -   (c) removing a defect-free shape cast article from the mold.        After the removing step, the method may optionally include:    -   (d) tempering the shape cast article (e.g., tempering to a T5,        T6 or T7 temper).        Defect-free means that the shape-cast article can be used for        its intended purpose.

Regarding the introducing step (b), the mold may be any suitable moldcompatible with the new aluminum casting alloy, such as a high pressuredie casting (HPDC) mold.

Prior to the removing step (c), the method may include allowing thecasting to solidify, and then cooling the casting. In one embodiment,the cooling step includes contacting the shape casting with water afterthe solidifying step. In another embodiment, the cooling step includescontacting the shape casting with air and/or water after the solidifyingstep. After the removing step (c), the method may include tempering theshape cast article.

In one embodiment, the tempering is tempering to a T5 temper. As definedby ANSI H35.1 (2009), the T5 temper is where an aluminum alloy is“cooled from an elevated temperature shaping process and thenartificially aged. Applies to products that are not cold worked aftercooling from an elevated temperature shaping process, or in which theeffect of cold work in flattening or straightening may not be recognizedin mechanical property limits.” When tempering to a T5 temper, thetempering step may include, after the removing step, artificially agingthe shape cast article. The artificially aging may be accomplished asdescribed below. Due to the shape casting process (e.g., HPDC), the T5temper does not require a separate solution heat treatment and quench(i.e., is free of a separate solution heat treatment and quenching step,as are required by the T6 and T7 temper.

In another embodiment, the tempering is tempering to a T6 temper. Asdefined by ANSI H35.1 (2009), the T6 is where an aluminum alloy is“solution heat-treated and then artificially aged. Applies to productsthat are not cold worked after solution heat-treatment, or in which theeffect of cold work in flattening or straightening may not be recognizedin mechanical property limits.” When tempering to a T6 temper, thetempering step (d) may include (i) solutionizing of the shape castarticle and subsequent (ii) quenching of the shape cast article. Afterthe quenching step (ii), the method may include (iii) artificial agingof the shape cast article.

In yet another embodiment, the tempering is tempering to a T7 temper. Asdefined by ANSI H35.1 (2009), the T7 is where an aluminum alloy is“solution heat-treated and overaged/stabilized. Applies to cast productsthat are artificially aged after solution heat-treatment to providedimensional and strength stability.” When tempering to a T7 temper, thetempering step (d) may include (i) solutionizing of the shape castarticle and subsequent (ii) quenching of the shape cast article. Afterthe quenching step (ii), the method may include (iii) artificially agingof the shape cast article to an overaged/stabilized condition.

In one approach, a method includes solution heat treating and quenchingthe aluminum alloy. In one embodiment, the solution heat treatingcomprises the steps of:

-   -   (a) heating the aluminum alloy to a first temperature (e.g.,        subjecting the alloy to a 2 hour±15 minutes heat-up from ambient        temperature up to 504.4° C.±5.0° C.);    -   (b) first maintaining the first temperature (e.g., for at least        0.5-8 hours, such as for about 2 hours);    -   (c) ramping the temperature to a second higher temperature        (e.g., ramping to 530° C.±5.0° C. and over a period of 5-60        minutes, such as ramping to the second temperature in about 30        minutes);    -   (d) second maintaining the second temperature at 530° C. (e.g.,        for 2-8 hours, such as holding for about 4 hours).

After the second maintaining step (d), the aluminum alloy may bequenching (e.g., in water and/or air).

As noted above, the tempering step may include artificially aging thealuminum alloy. In one embodiment, the artificially aging comprisesholding the alloy at a temperature of from 190° C. to 220° C. for 1-10hours (e.g., for about 6 hours). In another embodiment, the artificialaging is conducted at a temperature of from 175° C. to 205° C. for 1-10hours (e.g., for about 6 hours).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of phase equilibria involving (Al) and liquid in anAl—Cu—Mg—Si system.

FIG. 2 is a graph of the effect of Cu additions on the solidificationpath of Al-9% Si-0.4% Mg-0.1% Fe alloy.

FIG. 3 is a graph of the effect of Cu content on phase fractions inAl-9%-0.4% Mg-0.1% Fe-x % Cu alloys.

FIG. 4 is a graph of the effect of Cu and Mg content on the Q-phaseformation temperature of Al-9% Si—Mg—Cu alloys.

FIG. 5 is a graph of the effect of Mg and Cu content on the equilibriumsolidus temperature of Al-9% Si—Mg—Cu alloys.

FIG. 6 is a graph of the effect of Mg and Cu content on the equilibriumsolidus temperature (T_(S)) and Q-phase formation temperature (T_(Q)) ofAl-9% Si—Mg—Cu alloys.

FIG. 7 is a graph of the effect of zinc and silicon on the fluidity ofAl-x % Si-0.5% Mg-y % Zn alloys

FIG. 8 is an SEM (scanning electron micrograph) @200× magnification,showing spherical Si particles and un-dissolved Fe-containing particles.

FIGS. 9a-b are photographs of undissolved Fe-containing particles in theinvestigated alloys.

FIGS. 10a-d are graphs of the effect of aging condition on tensileproperties of the Al-9Si-0.5Mg alloy.

FIGS. 11a-d are graphs of the effect of Cu on tensile properties of theAl-9% Si-0.5% Mg alloy.

FIGS. 12a-d are graphs of the effect of Cu and Zn on tensile propertiesof the Al-9% Si-0.5% Mg alloy.

FIGS. 13a-d are graphs of the effect of Mg content on tensile propertiesof the Al-9% Si-1.25% Cu—Mg alloy.

FIGS. 14a-d are graphs of the effect of Ag on tensile properties of theAl-9% Si-0.35% Mg-1.75% Cu alloy.

FIGS. 15a-d are graphs of tensile properties for six alloys aged fordifferent times at an elevated temperature, as described in thedisclosure.

FIG. 16 is a graph of Charpy impact energy (CIE) vs. yield strength forfive alloys aged for different times at an elevated temperature.

FIG. 17 is a graph of S-N fatigue curves of selected alloys aged at 155°C. for 15 hours. Smooth, Axial; stress ratio=−1.

FIG. 18 is a graph of S-N fatigue curves of selected alloys aged at 155°C. for 60 hours. Smooth, Axial; stress ratio=−1.

FIG. 19a-d-23a-d are optical micrographs of cross-sections of samples offive alloys as cast and machined and aged for two different time periodsat an elevated temperature after 6-hour ASTM G110.

FIG. 24 is a graph of depth of attack of selected alloys aged fordifferent time periods on the as-cast and machined surfaces after a6-hour G110 test.

FIG. 25 is a graph of Mg and Cu content correlated to strength andductility for Al-9Si—Mg—Cu alloys.

FIG. 26 is a graph of tensile properties of a specific alloy (alloy 9)after exposure to high temperatures.

FIGS. 27a and 27b are scanning electron micrographs of a cross-sectionof a sample of alloy 9 prior to exposure to high temperatures.

FIGS. 28a-e are a series of scanning electron micrographs of across-section of alloy 9 after exposure to increasing temperaturescorrelated to a tensile property graph of alloy 9 and A356 alloy.

FIG. 29 is a graph of yield strength at room temperature for variousalloys.

FIG. 30 is a graph of yield strength after exposure to 175° C. forvarious alloys.

FIG. 31 is a graph of yield strength after exposure to 300° C. forvarious alloys.

FIG. 32 is a graph of yield strength after exposure to 300° C. forvarious alloys.

FIG. 33 is a graph of yield strength after exposure to 300° C. forvarious alloys.

FIG. 34 is a graph of yield strength after exposure to 300° C. forvarious alloys.

EXAMPLE 1 High Performance AlSiCuMg Cast Alloys 1.1 Alloy DevelopmentMethods Based on Computational Thermodynamics

To improve the performances of Al—Si—Mg—Cu cast alloys, a novel alloydesign method was used and is described as follows:

In Al—Si—Mg—Cu casting alloys, increasing Cu content can increase thestrength due to higher amount of θ′-Al₂Cu and Q′ precipitates but reduceductility, particularly if the amount of un-dissolved constituentQ-phase increases. FIG. 1 shows the calculated phase diagram of theAl—Cu—Mg—Si quaternary system, as shown in X. Yan, Thermodynamic andsolidification modeling coupled with experimental investigation of themulticomponent aluminum alloys. University of Wisconsin—Madison, 2001,which is incorporated in its entirety by reference herein. FIG. 1 showsthe three phase equilibria in ternary systems and the four phaseequilibria quaternary monovariant lines. Points A, B, C, D, E and F arefive phase invariant points in the quaternary system. Points T1 to T6are the four-phase invariant points in ternary systems and B1, B2 and B3are the three phase invariant points in binary systems. The formation ofQ-phase (AlCuMgSi) constituent particles during solidification is almostinevitable for an Al—Si—Mg alloy containing Cu since Q-phase is involvedin the eutectic reaction (invariant reaction B). If these Cu-containingQ-phase particles cannot be dissolved during solution heat treatment,the strengthening effect of Cu will be reduced and the ductility of thecasting will also suffer.

In order to minimize/eliminate un-dissolved Q-phase (AlCuMgSi) andmaximize solid solution/precipitation strengthening, the alloycomposition, solution heat treatment and aging practice should beoptimized. In accordance with the present disclosure, a thermodynamiccomputation was used to select alloy composition (mainly Cu and Mgcontent) and solution heat treatment for avoiding un-dissolved Q-phaseparticles. Pandat thermodynamic simulation software and the PanAluminumdatabase LLC, Computherm, Pandat Software and PanAluminum Database.http://www.computherm.com were used to calculate these thermodynamicdata.

The inventors of the present disclosure recognize that adding Cu toAl—Si—Mg cast alloys will change the solidification sequence. FIG. 2shows the predicted effect of 1% Cu (all compositions in this report arein weight percent) on the solidification path of Al-9% Si-0.4% Mg-0.1%Fe. More particularly, the solidification temperature range issignificantly increased with the addition of 1% Cu due to the formationof Cu-containing phases at lower temperatures. For the Al-9% Si-0.4%Mg-0.1% Fe-1% Cu alloy, Q-AlCuMgSi formed at ˜538° C. and θ—Al₂Cu phaseformed at ˜510° C. The volume fraction of each constituent phase andtheir formation temperatures are also influenced by the Cu content.

FIG. 3 shows the predicted effect of Cu content on phase fractions inAl-9% Si-0.4% Mg-0.1% Fe-x % Cu alloys. As the Cu content increases, theamount of θ-Al₂Cu and Q-AlCuMgSi increases while the amount of Mg₂Si andπ-AlFeMgSi decreases. In alloys with more than 0.7% Cu, Mg₂Si phase willnot form during solidification. The amount of Q-AlCuMgSi is also limitedby the Mg content in the alloy if the Cu content is more than 0.7%.

The Q-AlCuMgSi phase formation temperature (T_(Q)) in Al-9% Si—Mg—Cualloys is a function of Cu and Mg content. The “formation temperature”of a constituent phase is defined as the temperature at which theconstituent phase starts to form from the liquid phase. FIG. 4 shows thepredicted effects of Cu and Mg content on the formation temperature ofQ-AlCuMgSi phase. The formation temperature of Q-AlCuMgSi phasedecreases with increasing Cu content; but increases with increasing Mgcontent.

In accordance with the present disclosure, in order to completelydissolve all the as-cast Q-AlCuMgSi phase particles, the solution heattreatment temperature (T_(H)) needs to be controlled above the formationtemperature of the Q-AlCuMgSi phase, i.e., T_(H)>T_(Q). The upper limitof the solution heat treatment temperature is the equilibrium solidustemperature (T_(S)) in order to avoid re-melting. As a practicalmeasure, the solution heat treatment temperature is controlled to be atleast 5 to 10° C. below the solidus temperature to avoid localizedmelting and creation of metallurgical flaws known in the art asrosettes. Hence, in practice, the following relationship is established:

T _(S)−10° C.>T _(H) >T _(Q)   (1)

In accordance with the present disclosure, to achieve this criterion,the alloy composition, mainly the Cu and Mg contents, should be selectedso that the formation temperature of Q-AlCuMgSi phase is lower than thesolidus temperature. FIG. 5 shows the predicted effects of Cu and Mgcontent on the solidus temperature of Al-9% Si—Cu—Mg alloys. Asexpected, the solidus temperature decreases as the Cu and Mg contentincreases. It should be noted that Mg content increases the formationtemperature of the Q-AlCuMgSi phase but decreases the solidustemperature as indicated in FIG. 6. The Q-AlCuMgSi phase formationtemperature surface and the (T_(S)−10° C.) surface (10° C. below thesolidus temperature surface) are superimposed in FIG. 6. These twosurfaces intersect along the curve A-B-C. The area that meets thecriterion of Equation (1) is on the right hand side of curve A-B-C,i.e., T_(Q)<T_(S)−10° C. Projection of the curve A-B-C to the Cu—Mgcomposition plane yields the center line Cu+10Mg=5.25 of the preferredcomposition boundary, as shown in FIG. 25. The lower boundary,Cu+10Mg=4.73, was defined by the intersection of the Q-AlCuMgSi phaseformation temperature surface and the (T_(S)−15° C.) surface (15° C.below the solidus temperature surface). The upper boundary,Cu+10Mg=5.78, was defined by the intersection of the Q-AlCuMgSi phaseformation temperature surface and the (T_(S)−5° C.) surface (5° C. belowthe solidus temperature surface). For Al-9% Si-0.1% Fe-x % Cu-y % Mgalloys, Q-AlCuMgSi phase particles can be completely dissolved duringsolution heat treatment when the Cu and Mg contents are controlledwithin these boundaries.

In accordance with the present disclosure, the preferred Mg and Cucontent to maximize the alloy strength and ductility is shown in FIG.25.

The preferred relationship of Mg and Cu content is defined by:

Cu+10Mg=5.25 with 0.5<Cu<2.0

The upper bound is Cu+10Mg=5.8 and the lower bound is Cu+10Mg=4.7.

The foregoing approach allows the selection of a solutionizationtemperature by (i) calculating the formation temperature of alldissolvable constituent phases in an aluminum alloy; (ii) calculatingthe equilibrium solidus temperature of an aluminum alloy; (iii) defininga region in Al—Cu—Mg—Si space where the formation temperature of alldissolvable constituent phases is at least 10° C. below the solidustemperature. The Al—Cu—Mg—Si space is defined by the relative %composition of each of Al, Cu, Mg and Si and the associated solidustemperatures for the range of relative composition. For a given class ofalloy, e.g., Al—Cu—Mg—Si, the space may be defined by the solidustemperature associated with relative composition of two elements ofinterest, e.g., Cu and Mg, which are considered relative to their impacton the significant properties of the alloy, such as tensile properties.In addition, the solutionizing temperature may be selected to diminishthe presence of specific phases, e.g., that have a negative impact onsignificant properties, such as, tensile properties. The alloy, e.g.,after casting, may be heat treated by heating above the calculatedformation temperature of the phase that needs to be completely dissolvedafter solution heat treatment, e.g., the Q-AlCuMgSi phase, but below thecalculated equilibrium solidus temperature. The formation temperature ofthe phase that needs to be completely dissolved after solution heattreatment and solidus temperatures may be determined by computationalthermodynamics, e.g., using Pandat™ software and PanAluminum™ Databaseavailable from CompuTherm LLC of Madison, Wis.

1.2 Composition Selection for Tensile Bar Casting

Based on the foregoing analysis, several Mg and Cu content combinationswere selected as given in Table 3. Additionally, studies by the presentinventors have indicated that an addition of zinc with a concentrationgreater than 3 wt % to Al—Si—Mg—(Cu) alloys can increase both ductilityand strength of the alloy. As shown in FIG. 7, zinc can also increasethe fluidity of Al—Si—Mg alloys. Thus, an addition of zinc (4 wt %) wasalso evaluated. It has also been reported L. A. Angers, Development ofAdvanced I/M 2xxx Alloys for High Speed Civil Transport Applications,Alloy Technology Division Report No. AK92, 1990-04-16 that an additionof Ag can accelerate age-hardening of high Cu-containing (>˜1.5 wt %)aluminum alloys, and increase the tensile strength at room temperatureand elevated temperature. An addition of Ag (0.5 wt %) was also includedin alloys with higher Cu content such as 1.75 wt % Cu. Hence, ten alloycompositions were selected for evaluation. The target compositions ofthese alloys are given in Table 3. It should be noted that alloy 1 inTable 3 is the baseline alloy, A359.

TABLE 3 Target Compositions (all values in weight percent) Alloy Si CuMg Zn Ag Fe Sr* Ti B 1 Al—9Si—0.5Mg 9 0 0.5 0 0 <0.1 0.0125 0.04 0.003 2Al—9Si—0.35Mg—0.75Cu—4Zn 9 0.75 0.35 4 0 <0.1 0.0125 0.04 0.003 3Al—9Si—0.45Mg—0.75Cu—4Zn 9 0.75 0.45 4 0 <0.1 0.0125 0.04 0.003 4Al—9Si—0.45Mg—0.75Cu 9 0.75 0.45 0 0 <0.1 0.0125 0.04 0.003 5Al—9Si—0.5Mg—0.75Cu 9 0.75 0.5 0 0 <0.1 0.0125 0.04 0.003 6Al—9Si—0.35Mg—1.25Cu 9 1.25 0.35 0 0 <0.1 0.0125 0.04 0.003 7Al—9Si—0.45Mg—1.25Cu 9 1.25 0.45 0 0 <0.1 0.0125 0.04 0.003 8Al—9Si—0.55Mg—1.25Cu 9 1.25 0.55 0 0 <0.1 0.0125 0.04 0.003 9Al—9Si—0.35Mg—1.75Cu 9 1.75 0.35 0 0 <0.1 0.0125 0.04 0.003 10Al—9Si—0.35Mg—1.75Cu—0.5Ag 9 1.75 0.35 0 0.5 <0.1 0.0125 0.04 0.003

A modified ASTM tensile-bar mold was used for the casting. A lubricatingmold spray was used on the gauge section, while an insulating mold spraywas used on the remaining portion of the cavity. Thirty castings weremade for each alloy. The average cycle time was about two minutes. Theactual compositions investigated are listed in Table 4, below.

TABLE 4 Actual Compositions (all values in weight percent) Alloy Si CuMg Zn Ag Fe Sr* Ti B 1 Al—9Si—0.5Mg 8.87 0.021 0.48 0 0 0.079 0.01250.05 0.003 2 Al—9Si—0.35Mg—0.75Cu—4Zn 9.01 0.75 0.37 4.03 0 0.077 0.01250.031 0.003 3 Al—9Si—0.45Mg—0.75Cu—4Zn 9.09 0.75 0.46 4.02 0 0.0810.0125 0.04 0.003 4 Al—9Si—0.45Mg—0.75Cu 9.18 0.76 0.45 0 0 0.083 0.01250.042 0.003 5 Al—9Si—0.5Mg—0.75Cu 9.02 0.77 0.49 0 0 0.081 0.0125 0.0130.003 6 Al—9Si—0.35Mg—1.25Cu 9.02 1.25 0.34 0 0 0.088 0.0125 0.03 0.0037 Al—9Si—0.45Mg—1.25Cu 9.11 1.28 0.44 0 0 0.082 0.0125 0.04 0.003 8Al—9Si—0.55Mg—1.25Cu 8.99 1.27 0.53 0 0 0.1 0.0125 0.04 0.003 9Al—9Si—0.35Mg—1.75Cu 9.29 1.83 0.37 0 0 0.08 0.0125 0.048 0.003 10Al—9Si—0.35Mg—1.75Cu—0.5Ag 8.88 1.78 0.35 0 0.5 0.081 0.0125 0.044 0.003The actual compositions are very close to the target compositions. Thehydrogen content (single testing) of the castings is given in Table 5.

TABLE 5 Hydrogen Content of the Castings Alloy H Content (ppm) 1Al—9Si—0.5Mg 0.14 2 Al—9Si—0.35Mg—0.75Cu—4Zn 0.11 3Al—9Si—0.45Mg—0.75Cu—4Zn 0.19 4 Al—9Si—0.45Mg—0.75Cu 0.11 5Al—9Si—0.5Mg—0.75Cu 0.14 6 Al—9Si—0.35Mg—1.25Cu 0.15 7Al—9Si—0.45Mg—1.25Cu 0.13 8 Al—9Si—0.55Mg—1.25Cu 0.16 9Al—9Si—0.35Mg—1.75Cu 0.13 10 Al—9Si—0.35Mg—1.75Cu—0.5Ag Not measuredNote: alloy 3 was degassed with porous lance; all other alloys weredegassed using a rotary degasser.

1.3 The Preferred Solution Heat Treat Temperature as a Function of Cuand Mg

To dissolve all the Q-AlCuMgSi phase particles, the solution heattreatment temperature should be higher than the Q-AlCuMgSi phaseformation temperature. Table 6 lists the calculated final eutectictemperature, Q-phase formation temperature and solidus temperature usingthe targeted composition of the ten alloys investigated.

TABLE 6 Calculated Final Eutectic Temperature, Q-phase FormationTemperature and Solidus Temperature for Ten Investigated Casting AlloysFinal eutectic Q-phase Solidus temper- forming temper- ature,temperature, ature, Alloy ° C. ° C. ° C. 1 Al—9Si—0.5Mg 560 — 563 2Al—9Si—0.35Mg—0.75Cu—4Zn 470 518 540 3 Al—9Si—0.45Mg—0.75Cu—4Zn 470 518543 4 Al—9Si—0.45Mg—0.75Cu 510 541 554 5 Al—9Si—0.5Mg—0.75Cu 510 541 5536 Al—9Si—0.35Mg—1.25Cu 510 533 552 7 Al—9Si—0.45Mg—1.25Cu 510 536 548 8Al—9Si—0.55Mg—1.25Cu 510 538 545 9 Al—9Si—0.35Mg—1.75Cu 510 528 543 10Al—9Si—0.35Mg—1.75Cu—0.5Ag 510 526 543Based on the above mentioned information, two solution heat treatmentpractices were defined and used. Alloys 2, 3, 9 and 10 had lower solidustemperature and/or lower final eutectic/Q-phase formation temperaturethan others. Hence a different SHT practice was used.

The practice I for alloys 2, 3, 9 and 10 was:

-   -   1.5 hour log heat-up to 471° C.    -   2 hour soak at 471° C.    -   0.5 hour ramp up to 504° C.    -   4 hour soak at 504° C.    -   0.5 hour ramp up to T_(H)    -   6 hour soak at T_(H)    -   CWQ (Cold Water Quench)        and practice II for other six alloys was:    -   1.5 hour log heat-up to 491° C.    -   2 hour soak at 491° C.    -   0.25 hour ramp up to 504° C.    -   4 hour soak at 504° C.    -   0.5 hour ramp up to T_(H)    -   6 hour soak at T_(H)    -   CWQ (Cold Water Quench)        The final step solution heat treatment temperature T_(H) was        determined from following equation based on Mg and Cu content:

T _(H)(° C.)=570−10.48*Cu−71.6*Mg−1.3319*Cu*Mg−0.72*Cu*Cu+72.95*Mg*Mg,  (2)

where, Mg and Cu are magnesium and copper contents, in wt. %. A lowerlimit for T_(H) is defined by:

T _(Q)=533.6−20.98*Cu+88.037*Mg+33.43*Cu*Mg−0.7763*Cu*Cu−126.267*Mg*Mg  (3)

An upper limit for T_(H) is defined by:

T _(S)=579.2−10.48*Cu−71.6*Mg−1.3319*Cu*Mg−0.72*Cu*Cu+72.95*Mg*Mg   (4)

The microstructure of the solution heat treated specimens wascharacterized using optical and SEM microscopy. There were noun-dissolved Q-phase particles detected in all the Cu-containing alloysinvestigated. FIG. 8 shows the microstructure of the Al-9% Si-0.35%Mg-1.75% Cu alloy (alloy #9) in the T6 temper. Si particles were allwell-spheroidized. Some un-dissolved particles were identified asβ-AlFeSi, π-AlFeMgSi and Al₇Cu₂Fe phases. The morphologies of theseun-dissolved phases are shown in FIG. 9 at higher magnification.

1.4 Experimental Results 1.4.1 Property Characterization

Tensile properties were evaluated according to the ASTM B557 method.Test bars were cut from the modified ASTM B108 castings and tested onthe tensile machine without any further machining All the tensileresults are an average of five specimens. Toughness of selected alloyswas evaluated using the un-notched Charpy Impact test, ASTM E23-07a. Thespecimen size was 10 mm×10 mm×55 mm machined from the tensile-barcasting. Two specimens were measured for each alloy.

Smooth S-N fatigue test was conducted according to the ASTM E606 method.Three stress levels, 100 MPa, 150 MPa, and 200 MPa were evaluated. The Rratio was −1 and the frequency was 30 Hz. Three replicated specimenswere tested for each condition. Test was terminated after about 10⁷cycles. Smooth fatigue round specimens were obtained by slightlymachining the gauge portion of the tensile bar casting.

Corrosion resistance (type-of-attack) of selected conditions wasevaluated according to the ASTM G110 method. Corrosion mode anddepth-of-attack on both the as-cast surface and machined surface wereassessed.

All the raw test data including tensile, Charpy impact and S-N fatigueare given in Tables 7 to 9. A summary of the findings is given in thefollowing sections.

TABLE 7 Mechanical properties of various alloys aged at 155° C. fordifferent times* Aged at Aged at 155° C. for 15 hrs 155° C. for 30 hrsUTS TYS E Q UTS TYS E Q Alloy (MPa) (MPa) (%) (MPa) (MPa) (MPa) (%)(MPa) 1. Al—9Si—0.5Mg 405.8 323.3 8.3 543.2 398.5 326.5 6.5 520.4 2.Al—9Si—0.35Mg—0.75Cu—4Zn 431.5 342.0 5.5 542.6 433.5 358.0 4.5 531.5 3.Al—9Si—0.45Mg—0.75Cu—4Zn 460.5 370.5 5.5 571.6 469.0 378.5 7.0 595.8 4.Al—9Si—0.45Mg—0.75Cu 451.5 339.0 6.5 573.4 450.5 354.8 5.0 555.3 5.Al—9Si—0.5Mg—0.75Cu 426.0 317.3 8.0 561.5 442.8 348.2 6.7 566.4 6.Al—9Si—0.35Mg—1.25Cu 411.2 299.2 7.3 540.2 436.3 326.3 7.0 563.1 7.Al—9Si—0.45Mg—1.25Cu 424.3 328.0 4.8 525.8 453.8 353.0 5.8 567.7 8.Al—9Si—0.55Mg—1.25Cu 444.8 336.5 6.0 561.6 460.3 365.3 4.8 561.8 9.Al—9Si—0.35Mg—1.75Cu 465.7 325.0 9.0 608.8 459.5 355.3 5.5 570.6 10.Al—9Si—0.35Mg—1.75Cu—0.5Ag 463.3 343.0 7.5 594.5 471.7 364.5 6.3 591.9Aged at 155° C. for 60 hrs Alloy UTS (MPa) TYS (MPa) E (%) Q (MPa) 1.Al—9Si—0.5Mg 398.7 340.2 5.3 507.7 2. Al—9Si—0.35Mg—0.75Cu—4Zn 446.8366.0 6.5 568.7 3. Al—9Si—0.45Mg—0.75Cu—4Zn 465.3 390.7 5.0 570.2 4.Al—9Si—0.45Mg—0.75Cu 464.0 373.5 6.5 585.9 5. Al—9Si—0.5Mg—0.75Cu 442.5364.5 6.0 559.2 6. Al—9Si—0.35Mg—1.25Cu 446.5 342.8 6.5 568.4 7.Al—9Si—0.45Mg—1.25Cu 455.3 375.8 4.0 545.6 8. Al—9Si—0.55Mg—1.25Cu 475.8385.0 4.8 577.3 9. Al—9Si—0.35Mg—1.75Cu 478.8 386.3 5.0 583.6 10.Al—9Si—0.35Mg—1.75Cu—0.5Ag 471.0 389.3 4.5 569.0 *Averaged value fromfive tensile specimens. The Quality Index, Q = UTS + 150 log(E).

TABLE 8 Charpy impact test results for some selected alloys Energy(ft-lbs) 155° C./15 hrs 155° C./60 hrs Speci- Speci- Speci- Speci- Alloymen 1 men 3 men 7 men 9 1. Al—9Si—0.5Mg 6 27 23 27 3.Al—9Si—0.45Mg—0.75Cu—4Zn 17 18 10 12 4. Al—9Si—0.45Mg—0.75Cu 32 15 28 137. Al—9Si—0.45Mg—1.25Cu 27 12 7 12 9. Al—9Si—0.35Mg—1.75Cu 16 15 8 9

TABLE 9 S-N fatigue results for some selected alloys aged at 155° C. for60 hours ( Smooth, Axial; stress ratio = −1) Cycles to Failure Stress155 C./ 155 C./ Alloy (MPa) 15 hrs 60 hrs 1. Al—9Si—0.5Mg 100 16807251231620 1. Al—9Si—0.5Mg 100 1302419 272832 1. Al—9Si—0.5Mg 100 43210291077933 1. Al—9Si—0.5Mg 150 71926 148254 1. Al—9Si—0.5Mg 150 24283342791 1. Al—9Si—0.5Mg 150 153073 56603 1. Al—9Si—0.5Mg 200 1600354623 1. Al—9Si—0.5Mg 200 8654 30708 1. Al—9Si—0.5Mg 200 36597 39376 3.Al—9Si—0.45Mg—0.75Cu—4Zn 100 160572 248032 3. Al—9Si—0.45Mg—0.75Cu—4Zn100 298962 131397 3. Al—9Si—0.45Mg—0.75Cu—4Zn 100 120309 394167 3.Al—9Si—0.45Mg—0.75Cu—4Zn 150 120212 12183 3. Al—9Si—0.45Mg—0.75Cu—4Zn150 70152 42074 3. Al—9Si—0.45Mg—0.75Cu—4Zn 150 190200 31334 3.Al—9Si—0.45Mg—0.75Cu—4Zn 200 38369 18744 3. Al—9Si—0.45Mg—0.75Cu—4Zn 20029686 14822 3. Al—9Si—0.45Mg—0.75Cu—4Zn 200 39366 11676 4.Al—9Si—0.45Mg—0.75Cu 100 485035 575446 4. Al—9Si—0.45Mg—0.75Cu 1004521553 233110 4. Al—9Si—0.45Mg—0.75Cu 100 3287495 940229 4.Al—9Si—0.45Mg—0.75Cu 150 170004 141654 4. Al—9Si—0.45Mg—0.75Cu 150110500 234640 4. Al—9Si—0.45Mg—0.75Cu 150 688783 238478 4.Al—9Si—0.45Mg—0.75Cu 200 108488 22686 4. Al—9Si—0.45Mg—0.75Cu 200 4000736390 4. Al—9Si—0.45Mg—0.75Cu 200 51678 20726 7. Al—9Si—0.45Mg—1.25Cu100 1115772 1650686 7. Al—9Si—0.45Mg—1.25Cu 100 318949 1744140 7.Al—9Si—0.45Mg—1.25Cu 100 468848 484262 7. Al—9Si—0.45Mg—1.25Cu 150102341 232171 7. Al—9Si—0.45Mg—1.25Cu 150 145766 106741 7.Al—9Si—0.45Mg—1.25Cu 150 63720 226188 7. Al—9Si—0.45Mg—1.25Cu 200 4168621873 7. Al—9Si—0.45Mg—1.25Cu 200 20709 58819 7. Al—9Si—0.45Mg—1.25Cu200 52709 4367 9. Al—9Si—0.35Mg—1.75Cu 100 2159782 2288145 9.Al—9Si—0.35Mg—1.75Cu 100 354677 1011473 9. Al—9Si—0.35Mg—1.75Cu 1004258369 783758 9. Al—9Si—0.35Mg—1.75Cu 150 281867 164554 9.Al—9Si—0.35Mg—1.75Cu 150 135810 188389 9. Al—9Si—0.35Mg—1.75Cu 150100053 146740 9. Al—9Si—0.35Mg—1.75Cu 200 24014 48506 9.Al—9Si—0.35Mg—1.75Cu 200 30695 8161 9. Al—9Si—0.35Mg—1.75Cu 200 6221131032

1.4.2 Mechanical Properties at Room Temperature 1.4.2.1 Effect of AgingTemperature on Tensile Properties

The effect of artificial aging temperature on tensile properties wasinvestigated using the baseline alloy 1-Al-9% Si-0.5% Mg. After aminimum 4 hours of natural aging, the tensile bar castings were aged at155° C. for 15, 30, 60 hours and at 170° C. for 8, 16, 24 hours. Threereplicate specimens were used for each aging condition.

FIG. 10 shows the tensile properties of the baseline A359 alloy (Al-9%Si-0.5% Mg) at various aging conditions. Low aging temperature (155° C.)tends to yield higher quality index than the high aging temperature(170° C.). Thus, the low aging temperature at 155° C. was selected, eventhough the aging time is longer to obtain improved properties.

1.4.2.2 Effects of Alloy Elements on Tensile Properties

FIG. 11 compares the tensile properties of baseline Al-9% Si-0.5% Mgalloy and Al-9% Si-0.5% Mg-0.75% Cu alloy. The addition of 0.75% Cu toAl-9% Si-0.5% Mg alloy increases the yield strength by ˜20 MPa andultimate tensile strength by ˜40 MPa while maintaining the elongation.The average quality index of the Cu-containing alloy is ˜560 MPa, whichis much higher than the baseline alloy with an average of ˜520 MPa.

FIG. 12 compares the tensile properties of four cast alloys, 1, 2, 3 and4. Alloy 1 is the baseline alloy. Alloy 2-4 all contain 0.75% Cu withvarious amounts of Mg and/or Zn. Alloys 3 and 4 contain 0.45% Mg, whilealloy 2 contains 0.35% Mg and alloy 1 contains 0.5% Mg. Alloys 2 and 3also have 4% Zn. A preliminary assessment of these four alloys indicatesthat Mg and Zn increase alloy strength without sacrificing ductility. Adirect comparison between alloys 3 and 4 indicates that by adding 4% Znto the Al-9% Si-0.45% Mg-0.75% Cu alloy, both ultimate tensile strengthand yield strength are increased while maintaining the elongation. The4% Zn addition also increases the aging kinetics as indicated in FIG.12. When aged at 155° C. for 15 hours, yield strength of about 370 MPacan be achieved for the Al-9% Si-0.45% Mg-0.75% Cu-4% Zn alloy, which isabout 30 MPa higher than that of the alloy without Zn.

FIG. 13 shows the effect of Mg content (0.35-0.55wt %) on the tensileproperties of the Al-9% Si-1.25% Cu—Mg alloys (Alloys 6-8). The tensileproperties of the baseline alloy Al-9% Si-0.5% Mg are also included forcomparison. Mg content showed significant influence on the tensileproperties. With increasing Mg content, both yield strength and tensilestrength were increased, but the elongation was decreased. The decreaseof elongation with increasing Mg content could be related to higheramount of π-AlFeMgSi phase particles even if all the Q-AlCuMgSi phaseparticles were dissolved. The impact of Mg content on quality indexes ofthe Al-9% Si-1.25% Cu—Mg alloys was overall found to be insignificant.

FIG. 14 shows the effect of Ag (0.5wt %) on the tensile properties ofAl-9% Si-0.35% Mg-1.75% Cu alloy. An addition of 0.5wt % Ag had verylimited impact on strength, elongation and quality index of the Al-9%Si-0.35% Mg-1.75% Cu alloy. It should be noted that the quality index ofthe Al-9% Si-0.35% Mg-1.75% Cu (without Ag) alloy is ˜60 MPa higher thanthe baseline alloy, A359 (Alloy 1).

FIGS. 15a-15d show the tensile properties of five promising alloys inaccordance with the present disclosure along with the baseline alloyAl-9Si-0.5 Mg (alloy 1). These five alloys achieve the target tensileproperties, i.e., 10-15% increase in tensile and maintaining similarelongation as A356/A357 alloy. The alloys are: Al-9% Si-0.45% Mg-0.75%Cu (Alloy 4), Al-9% Si-0.45% Mg-0.75% Cu-4%Zn(Alloy 3), Al-9% Si-0.45%Mg-1.25% Cu (Alloy 7), Al-9% Si-0.35% Mg-1.75% Cu (Alloy 9), and Al-9%Si-0.35% Mg-1.75% Cu-0.5% Ag (Alloy 10).

Based on the data, it is believed that the following tensile propertiescan be obtained with alloys aged at 155° C. for time ranged from 15 to60 hrs.

Ultimate tensile strength: 450-470 MPa Tensile yield strength: 360-390MPa Elongation:  5-7% Quality index: 560-590 MPa

These properties are much higher than A359 (Alloy 1) and are verysimilar to A201 (Al4.6Cu0.35Mg0.7Ag) cast alloy (UTS 450 MPa, TYS 380MPa, Elongation 8%, and Q 585 MPa) ASM Handbook Volume 15, Casting, ASMInternational, December 2008. On the other hand, the castability ofthese Al-9% Si—Mg—Cu alloys is much better than A201 alloy. The A201alloy has a poor castability due to its high tendency of hot crackingand Cu macro-segregation. Additionally, the material cost of A201 with0.7wt % Ag is also much higher than those embodiments in accordance withthe present disclosure that are Ag-free.

Based on the tensile property results, four alloys without Ag (Alloys 3,4, 7 and 9) with promising tensile properties along with baseline alloy,A359 (Alloy 1) were selected for further investigation. Charpy impact,S-N fatigue and general corrosion tests were conducted on these fivealloys aged at 155° C. for 15 hours and 60 hours.

1.4.4 Charpy Impact Tests

FIG. 16 shows the results of the individual tests by plotting Charpyimpact energy vs. tensile yield strength. The filled symbols are forspecimens aged at 155° C. for 15 hours and open symbols are forspecimens aged at 155° C. for 60 hours. Tensile yield strength increasesas the aging time increases, while the Charpy impact energy decreaseswith increasing aging time. The results indicate that most alloys/agingconditions follow the expected strength/toughness relationship. However,the results indeed show a slight degradation of the strength/toughnessrelationship with higher Cu content such as 1.25 and 1.75wt %.

1.4.5 S-N Fatigue Tests

Aluminum castings are often used in engineered components subject tocycles of applied stress. Over their commercial lifetime millions ofstress cycles can occur, so it is important to characterize theirfatigue life. This is especially true for safety critical applications,such as automotive suspension components.

FIGS. 17 and 18 show the S-N fatigue test results of five selectedalloys aged at 155° C. for 15 and 60 hours, respectively. During thesetests a constant amplitude stress (R=−1) was applied to the testspecimens. Three different stress levels, 100 MPa, 150 MPa and 200 MPawere applied. The total number of cycles to failure was recorded.

When aged at 155° C. for 15 hours, all the Cu-containing alloys showedbetter fatigue performance (higher number of cycles to failure) than thebaseline A359 alloy at higher stress levels (>150 MPa). At lower stresslevels (<125 MPa), the fatigue lives of the Al-9Si-0.45Mg-0.75Cu andAl-9Si-0.35Mg-1.75Cu alloys are very similar to the A359 alloy, whilethe fatigue life of the Al-9Si-0.45Cu-0.75Cu-4Zn alloy (alloy 3) waslower than the A359 alloy. The lower fatigue life of this alloy couldresult from the higher hydrogen content of the casting, as statedpreviously.

Increasing aging time (higher tensile strength) tended to decrease thenumber of cycles to failure. For example, as the aging time increasedfrom 15 hours to 60 hours, the average number of cycles to failure at150 MPa stress level decreased from ˜323,000 to ˜205,000 for the Al-9%Si-0.45% Mg-0.75% Cu alloy and from ˜155,900 to ˜82,500 for the A359alloy. The result could be a general trend of the strength/fatiguerelationship of Al—Si—Mg—(Cu) casting alloys. Again, alloy 3 showed alower fatigue performance than others.

1.4.6 Corrosion Tests—ASTM G110

FIGS. 19 to 23 show optical micrographs of the cross-sectional viewsafter 6-hour ASTM G110 tests for five selected alloys of both theas-cast surfaces and machined surfaces. The mode of corrosion attack waspredominantly interdendritic corrosion. The number of corrosion siteswas generally higher in the four Cu-containing compositions than in theCu-free baseline alloy.

More particularly, FIGS. 19a-d show optical micrographs ofcross-sections of Al-9% Si-0.5% Mg after a 6-hour ASTM G110 test: a) ofthe alloy as cast and aged 15 hours at 155° C.; b) of the alloy as castand aged 60 hours at 155° C.; c) of the alloy with a machined surfaceand aged 15 hours at 155° C.; and d) of the alloy with a machinedsurface and aged 60 hours at 155° C.

FIGS. 20a-d show optical micrographs of cross-sections of Al-9% Si-0.35%Mg-0.75% Cu-4% Zn after a 6-hour ASTM G110 test: a) of the alloy as castand aged 15 hours at 155° C.; b) of the alloy as cast and aged 60 hoursat 155° C.; c) of the alloy with a machined surface and aged 15 hours at155° C.; and d) of the alloy with a machined surface and aged 60 hoursat 155° C.

FIGS. 21a-d show optical micrographs of cross-sections of Al-9% Si-0.45%Mg-0.75% Cu after a 6-hour ASTM G110 test: a) of the alloy as cast andaged 15 hours at 155° C.; b) of the alloy as cast and aged 60 hours at155° C.; c) of the alloy with a machined surface and aged 15 hours at155° C.; and d) of the alloy with a machined surface and aged 60 hoursat 155° C.

FIGS. 22a-d show optical micrographs of cross-sections of Al-9% Si-0.45%Mg-1.25% Cu after a 6-hour ASTM G110 test: a) of the alloy as cast andaged 15 hours at 155° C.; b) of the alloy as cast and aged 60 hours at155° C.; c) of the alloy with a machined surface and aged 15 hours at155° C.; and d) of the alloy with a machined surface and aged 60 hoursat 155° C.

FIGS. 23a-d show optical micrographs of cross-sections of Al-9% Si-0.35%Mg-1.75% Cu after a 6-hour ASTM G110 test: a) of the alloy as cast andaged 15 hours at 155° C.; b) of the alloy as cast and aged 60 hours at155° C.; c) of the alloy with a machined surface and aged 15 hours at155° C.; and d) of the alloy with a machined surface and aged 60 hoursat 155° C.

FIG. 24 shows the depth of attack after the 6-hour ASTM G110 test. Thereis no clear difference or trend among the alloys. Aging time did notshow obvious impact on the depth of attack either, while somedifferences were found between the as-cast surfaces and the machinedsurfaces. In general, the corrosion attack was slightly deeper on themachined surface than the as-cast surface of the same sample.

Overall, the additions of Cu or Cu+Zn do not change the corrosion modenor increase the depth-of—attack of the alloys. It is believed that allthe alloys evaluated have similar corrosion resistance as the baselinealloy, A359.

The present disclosure has described Al—Si—Cu—Mg alloys that can achievehigh strength without sacrificing ductility. Tensile propertiesincluding 450-470 MPa ultimate tensile strength, 360-390 MPa yieldstrength, 5-7% elongation, and 560-590 MPa Quality Index were obtained.These properties exceed conventional 3xx alloys and are very similar tothat of the A201 (2xx+Ag) Alloy, while the castabilities of the newAl-9Si—MgCu alloys are much better than that of the A201 alloy. The newalloys showed better S-N fatigue resistance than A359 (Al-9Si-0.5 Mg)alloys. Alloys in accordance with the present disclosure have adequatefracture toughness and general corrosion resistance.

EXAMPLE 2 Cast Alloys for Applications at Elevated Temperatures

Because alloys such as those described in the present disclosure may beutilized in applications wherein they are exposed to high temperatures,such as in engines in the form of engine blocks, cylinder heads,pistons, etc., it is of interest to assess how such alloys behave whenexposed to high temperatures. FIG. 26 shows a graph of tensileproperties of an alloy in accordance with the present disclosure,namely, Al-9Si-0.35Mg-1.75Cu (previously referred to as alloy 9, e.g.,in FIG. 15) after exposure to various temperatures. As noted, for eachtest generating data in the graph, the exposure time of the alloys was500 hours at the indicated temperature. The samples were also tested atthe temperature indicated. As shown in the graph, the yield strength ofthe alloy diminished significantly at temperatures above 150° C. Inaccordance with the present disclosure, the metal was analyzed toascertain features associated with the loss in strength due to exposureto increased temperatures.

FIGS. 27a and 27b show scanning electron microscope (SEM) micrographs ofa cross-section of a sample of alloy 9 prior to exposure to hightemperatures, with 27 b being an enlarged view of the portion of themicrograph of 31a indicated as “Al”. As shown in FIG. 27a , the grainboundaries are visible, as well as, Si and AlFeSi particles. Thepredominately Al portion shown in FIG. 27b shows no visible precipitateat 20,000× magnification.

FIGS. 28a-e show a series of scanning electron microscope (SEM)micrographs of a cross-section of alloy C00 (previously referred to asalloy 9, e.g., in FIG. 15) of the same scale as the micrograph shown inFIG. 27b after exposure to increasing temperatures as shown by thecorrelation of the micrographs to the data points on the tensileproperty graph G of alloy 9. The tensile characteristics of A356 alloyin the given temperature range are also shown in graph G for comparison.As can be appreciated from the sequence of micrographs, exposure ofalloy 9 to increasing temperatures results in continuously increasingprominence of precipitate particles, which are larger, and which exhibitdivergent geometries.

The inventors of the present disclosure recognized that certain alloyingelements, viz., Ti, V, Zr, Mn, Ni, Hf, and Fe could be introduced to theC00 alloy (previously referred to as alloy 9, e.g., in FIG. 15) of thepresent disclosure in small amounts to produce an alloy that resistsstrength degradation at elevated temperatures.

The following table (Table 10) show 18 alloys utilizing additiveelements in small quantities to the C00 alloy (previously referred to asalloy 9, e.g., in FIG. 15) for the purpose of developing improvedstrength at elevated temperatures.

TABLE 10 Alloy Compositions (all values in weight percent) Alloy Fe SiMn Cu Mg Sr Ti B V Zr Ni Hf C00 0.08 9.29 0 1.83 0.37 0.0125 0.05 0 0 00 C01 0.15 9.3 0.002 1.82 0.002 0.008 0.11 0.0047 0.012 0.002 0 0 C020.15 9.35 0.002 1.82 0.39 0.008 0.11 0.0043 0.012 0.002 0 0 C03 0.159.05 0.002 1.77 0.37 0.007 0.11 0.0051 0.13 0.002 0 0 C04 0.16 8.950.002 1.77 0.36 0.006 0.1 0.0026 0.1 0.091 0 0 C05 0.16 8.86 0.002 1.760.36 0.005 0.1 0.0016 0.13 0.15 0 0 C06 0.16 8.54 0.002 1.72 0.35 0.0040.1 0.005 0.13 0.18 0 0 C07 0.16 9.31 0.15 1.8 0.34 0.004 0.11 0.00440.025 0.016 0 0 C08 0.16 9.32 0.16 1.84 0.34 0.004 0.11 0.0051 0.0250.017 0 0 C09 0.17 9.1 0.28 1.8 0.33 0.003 0.11 0.005 0.025 0.016 0 0C10 0.32 9.26 0.3 1.83 0.34 0.003 0.11 0.0045 0.024 0.017 0 0 C11 0.498.96 0.3 1.78 0.32 0.003 0.12 0.0055 0.11 0.016 0 0 C12 0.56 8.97 0.31.79 0.32 0.002 0.1 0.0039 0.11 0.12 0 0 C13 0.15 9.28 0.003 1.82 0.330.0125 0.1 0.005 0.001 0.002 0.28 0 C14 0.2 9.28 0.004 1.81 0.33 0.0040.1 0.0026 0.012 0.002 0.28 0 C15 0.31 9.27 0.03 1.82 0.33 0.004 0.10.0032 0.012 0.002 0.28 0 C16 0.32 9.14 0.1 1.79 0.32 0.003 0.1 0.00320.012 0.003 0.27 0.1 C17 0.32 8.88 0.12 1.75 0.3 0.003 0.1 0.0031 0.110.013 0.26 0.1 C18 0.32 8.89 0.14 1.76 0.3 0.003 0.1 0.003 0.11 0.0360.27 0.1

Table 11 shows the mechanical properties of the foregoing alloys, viz.,ultimate tensile strength (UTS), total yield strength (TYS) andElongation % at 300° C., 175° C. and room temperature (RT).

TABLE 11 Mechanical Properties at Various Temperatures 300° C. Alloy UTS(ksi) TYS (ksi) Elong. (%) C00 8.2 8.4 8.3 6 6.3 6 49 54 29.5 C01 9.39.5 9.6 6.5 6.4 6.7 63 54.5 49.5 C02 10 10.3 9 6.9 7.2 6.5 51.5 40.540.5 C03 8.8 10.2 10.6 6.8 7.2 7.5 52 43.5 56.5 C04 10.4 10.3 11.7 7.97.4 8 47.5 47 41.5 C05 10.8 10.7 11.1 8.5 8 8.2 47 41.5 36.5 C06 11 9.311.2 7.7 7.1 8.5 35 36 42.5 C07 10.5 10.6 10.3 8.1 8 7.7 53 40 43.5 C0810 9.7 10.6 7.5 6.7 7.9 39 40.5 36.5 C09 10.3 10.8 11.7 7.5 7.8 8.6 3535 36 C10 10.7 10.7 11.3 8.1 8 8.3 37 40 33 C11 11 11.3 10.5 7.9 8.1 7.727.5 30.5 34.5 C12 11.7 10.8 11.4 8.2 7.9 8.2 33 28.5 34.5 C13 10.2 99.4 7.5 6.9 7 45.5 53 40 C14 9.3 9.2 9.9 6.6 6.6 6.9 56 44 42.5 C15 109.8 10 7.2 7.2 7.2 46.5 32 31.5 C16 10.3 10.3 10.1 7.7 7.5 7.5 44.5 36.534.5 C17 10.5 9.4 10 7.5 7.2 7.2 46.5 42.5 29.5 C18 10.1 11.4 11.3 7.58.6 8.2 29 28.5 25.5 175° C. Alloy UTS (ksi) TYS (ksi) Elongation (%)C00 34.8 33.7 37.1 28.8 27.8 31 8.5 10.5 10.5 C01 28.1 31 29.4 21.4 23.721.8 16.6 24 14.9 C02 43.6 46.2 46.1 38 39.6 40.2 6.9 5.1 5.1 C03 44.943.1 45.4 40.6 37.4 39.8 0.6 7.4 4 C04 46.5 46.5 48.3 40.6 41 42.8 6.99.1 4.6 C05 40 47.4 47 35.4 40.7 39.9 2.9 5.1 5.1 C06 44.3 43.6 46.638.4 37.4 40.9 5.7 8 3.4 C07 48.3 46.7 43 41.6 40.8 38 6.3 2.3 6.9 C0849.3 41.8 42.6 41.2 36.5 36.6 6.3 2.3 6.9 C09 39 45.2 43.9 33.7 39.238.6 3.4 3.4 2.3 C10 35.7 43.6 48.6 30.9 37.3 41.9 2.3 3.4 2.3 C11 42.442.5 47.6 36.5 35.8 41.1 1.1 2.3 2.3 C12 37.9 37.3 37.3 35.3 31.7 31.21.1 1.7 4 C13 45.3 45.2 41.3 39.2 38.2 35 2.9 6.3 8 C14 34.3 38.6 45.732.3 32.4 39 0.6 9.1 5.1 C15 40.1 45.2 44.7 34.2 38.5 37.6 2.9 5.1 3.4C16 42.3 41.6 41.7 35.4 35.2 35.9 4 5.1 2.3 C17 42.6 38.4 39.5 21.8 3834.2 14.9 6.9 2.3 C18 37.2 41.4 41.5 35.1 34.6 34.7 1.1 5.1 3.4 RoomTemperature Alloy UTS (ksi) TYS (ksi) Elongation (%) C00 58.4 56.5 47.752.4 4 4 58.4 56.5 47.7 C01 37.7 38.4 20.1 20.9 9 12 37.7 38.4 20.1 C0260.2 56.7 46.2 3 3 60.2 56.7 C03 50.5 59.8 48.7 50.3 3 5.5 50.5 59.848.7 C04 58.7 57.5 49.7 48.1 3 1 58.7 57.5 49.7 C05 52.4 58.2 51.1 47.71 3 52.4 58.2 51.1 C06 57.9 59.1 48.2 48.8 3 4 57.9 59.1 48.2 C07 5758.3 48.1 3.5 3.5 57 58.3 48.1 C08 58.6 52 46.2 48.2 3.5 3 58.6 52 46.2C09 52 58.1 47.9 48.5 3 3 52 58.1 47.9 C10 55 55.6 47.7 49.6 3 3 55 55.647.7 C11 54.1 52.6 49.3 49.1 3 3 54.1 52.6 49.3 C12 50.2 52.7 48.5 50.61 1.5 50.2 52.7 48.5 C13 56.3 58.5 48.1 45.9 2.5 8 56.3 58.5 48.1 C1461.3 57.1 44.3 44.5 8 4 61.3 57.1 44.3 C15 56.7 55.8 45.9 47.1 4 4 56.755.8 45.9 C16 57.4 53.7 46.4 46 4 3 57.4 53.7 46.4 C17 57.2 56.1 47.146.9 3 3 57.2 56.1 47.1 C18 48.5 50.6 45.1 46.9 2 2 48.5 50.6 45.1

FIG. 29 shows a graph of yield strength at room temperature forforegoing alloys. A356 is shown for comparison. In addition, adepartment of energy (DOE) published target for strength improvement isshown for comparison [Predictive Modeling for Automotive Light weightingApplications and Advanced Alloy Development for Automotive andHeavy-Duty Engines, Issue by Department of Energy on Mar. 3, 2012]. Ascan be appreciated, the C00 alloy is comparable in strength at roomtemperature to alloys C02-C18, all of which substantially exceed thestrength of the A356 alloy and the DOE target properties. AlloyC01-without substantial quantities of Mg, has a far lower yieldstrength.

FIG. 30 is a graph of yield strength after exposure to 175° C. for 500hours for the foregoing alloys. The C00, as well as A356 are shown forcomparison. As can be appreciated, the C00 alloy substantially exceedsthe strength of the A356 alloy. Alloys C02-C18), all show markedimprovement over both A356 and C00.

FIG. 31 is a graph of yield strength after exposure to 300° C. for 500hours for the foregoing alloys. C00, as well as A356 are shown forcomparison. FIG. 32 shows is a graph of yield strength after exposure to300° C. for various alloys. More particularly, adjacent alloys (going inthe direction of the arrows) show the result of an additional element orthe increase in quantity of an element. The highest result in the graphof FIG. 32 is for C00+0.1T+0.16Fe+0.13V+0.15Zr. The addition of more Zr(to 0.18%) to this combination results in decreased performance.

FIG. 33 is a graph of yield strength after exposure to 300° C. forvarious alloys for 500 hours. The graphs show improvements due to theaddition of Ti, Fe and Mn to the C00 composition, with the maximumperformance noted relative to C00+0.11Ti+0.32Fe+0.3Mn. The addition of Vto the foregoing reduces performance and the further addition of 0.12 Zrbrings performance almost back to the maximum level.

FIG. 34 is a graph of yield strength after exposure to 300° C. forvarious alloys, i.e., due to the addition of elements to the C00composition. The optimal performance is noted relative toC00+0.1Ti+0.28Ni+0.32 Fe+0.14Mn+0.1Hf+0.11V+0.04Zr.

EXAMPLE 3 Cast Alloys for Semi-Permanent Mold Cylinder Head Applications

High strength at elevated temperature and very good castability make theC05 alloy (TABLE 10) an excellent candidate for cylinder headapplications, e.g., for internal combustion engines. Plant-scale trialsfor the C05 alloy (TABLE 10) were conducted. Cylinder head castings weremade using a gravity semi-permanent mold casting process. The actualcompositions are listed in Table 12.

TABLE 12 Actual Composition of Example 3 Alloys Alloy Si Fe Cu Mn Mg TiV Zr Sr B D1 8.97 0.12 1.91 0.13 0.38 0.11 0.085 0.085 0.01 0 D2 9.140.14 1.98 0.14 0.37 0.11 0.094 0.1 0.011 0.0011

Tensile specimen blocks were cut from the combustion chamber area. Theywere solution heat treated using following practice:

2-hr log to 940° F. (504.4° C.)+940° F.(504.4° C.)/2 hrs+30 minutes rampup to 986° F.(530° C.)+986° F.(530° C.)/4 hrs+CWQ

Three artificial aging practices, 190° C./6 hrs, 205° C./6 hrs and 220°C./6 hrs, were evaluated and the mechanical property results are shownin Table 13.

TABLE 13 Mechanical Properties of Example 3 Alloys Artificial AgingTensile Yield Ultimate Tensile Elongation Condition Strength (MPa)Strength (MPa) (%) 190° C./6 hrs 332 386 2 190° C./6 hrs 336 387 2 205°C./6 hrs 320 362 2 205° C./6 hrs 326 369 3 220° C./6 hrs 273 322 2 220°C./6 hrs 281 335 3The foregoing alloy compositions may also be used to form cylinder headsby high pressure die casting (HPDC) methods and using T5 temperingprocedures.

EXAMPLE 4 Cast Alloys for HPDC Engine Block Applications

In accordance with another embodiment of the present disclosure, thedisclosed aluminum alloys may be used to cast cylinder blocks, e.g., forinternal combustion engines. Since the engine block is the maincontributor to engine mass, use of the disclosed alloys for the engineblock may result in significant weight reduction, e.g., up to 45% weightreduction for gasoline engines, compared to engines made from cast-iron.Engines having lower mass translate into improved performance, betterfuel economy and reduced emissions. For mass engine production,high-pressure die-casting (HPDC) process is widely used for highproduction rates and reduced production costs.

HPDC engine block casting methods frequently employ T5 temper practices.The alloys of the present disclosure may be tempered using T5 practices.Note that this approach does not employ a high-temperature solution heattreatment and quench. In accordance with an embodiment of the presentdisclosure, six alloys having the compositions shown in Table 14 wereprepared, cast into a modified ASTM tensile bar mold.

TABLE 14 Actual Composition of Example 4 Alloys (weight percent) AlloySi Cu Mg Fe Mn Ti V Zr Sr B R1 9.32 0.55 0.22 0.13 0.48 0.13 0.13 0.140.012 0.002 R2 9.25 0.54 0.42 0.13 0.52 0.13 0.13 0.14 0.012 0.002 R39.24 1.02 0.21 0.16 0.53 0.13 0.12 0.10 0.012 0.002 R4 9.41 1.02 0.410.17 0.53 0.14 0.12 0.10 0.012 0.002 R5 9.14 1.53 0.22 0.16 0.53 0.110.12 0.12 0.012 0.002 R6 9.27 1.52 0.43 0.16 0.53 0.12 0.12 0.12 0.0120.002 The weight ratio of Fe:Mn for all alloys was from 0.25 to 0.32.

Sixty (60) tensile bar specimens were made for each composition. Afterthe specimens were completely solidified, half were water quenched, andthe other half were air cooled. The physical attributes of the resultantspecimens were then tested and are also described below. Three differentartificial aging practices, 175° C./6hrs, 190° C./6hrs and 205° C./6hrs, were evaluated for both water quenched and air-cooled specimens.

Tables 15, 16 and 17 list average yield strength, ultimate tensilestrength and elongation, respectively, for air-cooled specimens aged atdifferent conditions. Table 15 shows the effect of Cu, Mg and agingcondition on yield strength of the Al-9Si-0.15Fe-0.55Mn—Cu—Mg alloys.After being completely solidified, the tensile bar castings were cooledin the air. As shown in Table 15, Mg and Cu content showed significantimpact on yield strength. Alloys with 0.4% Mg and 1.0-1.5% Cu showedhigher yield strength than other alloys.

Table 16 shows the effect of Cu, Mg and aging condition on ultimatetensile strength of the Al-9Si-0.15Fe-0.55Mn—Cu—Mg alloys. After beingcompletely solidified, tensile bar castings were cooled in the air.Table 16 shows the effect of Cu, Mg and aging condition on elongation ofthe Al-9Si-0.15Fe-0.55Mn—Cu—Mg alloys. After being completelysolidified, tensile bar castings were cooled in the air. As shown inTables 16-17, increasing Mg and Cu will slightly increase UTS, anddecrease elongation. For air cooled specimens, the highest achievedyield strength in the T5 condition was about 190 MPa.

TABLE 15 Yield Strength for R1-R6 Alloys (Air Cool) at VariousArtificial Aging Conditions Average Tensile Yield Strength StandardDeviation 190° C./ 205° C./ 190° C./ 205° C./ Alloy 175° C./6 hrs 6 hrs6 hrs 175° C./6 hrs 6 hrs 6 hrs R1 150 178 172 6.2 9.0 23.4 R3 142 150149 1.4 3.4 1.4 R5 174 198 179 4.1 4.8 12.4 R2 179 167 185 2.1 13.1 2.1R4 188 197 194 0.7 2.1 6.9 R6 200 194 195 9.6 6.9 8.3

TABLE 16 Tensile Strength for R1-R6 Alloys (Air Cool) at VariousArtificial Aging Conditions Average Ultimate Tensile Strength StandardDeviation 190° C./ 205° C./ 190° C./ 205° C./ Alloy 175° C./6 hrs 6 hrs6 hrs 175° C./6 hrs 6 hrs 6 hrs R1 223 248 269 14.5 22.7 22.0 R3 241 240234 2.1 7.6 17.2 R5 263 251 229 3.4 19.3 33.8 R2 251 249 243 9.0 26.24.8 R4 243 234 249 26.2 19.3 9.6 R6 243 269 237 17.9 11.0 29.6

TABLE 17 Elongation for R1-R6 Alloys (Air Cool) at Various ArtificialAging Conditions Average Elongation Standard Deviation 190° C./ 205° C./190° C./ 205° C./ Alloy 175° C./6 hrs 6 hrs 6 hrs 175° C./6 hrs 6 hrs 6hrs R1 2.50 2.17 3.50 0.50 0.76 1.32 R3 2.83 2.33 2.00 0.29 0.29 0.87 R52.50 1.67 1.17 0.00 0.29 0.29 R2 2.17 2.67 1.83 0.58 0.29 0.29 R4 1.831.33 1.67 0.58 0.29 0.29 R6 1.33 1.50 1.50 0.29 0.87 0.50

Tables 18, 19 and 20 list average yield strength, ultimate tensilestrength and elongation, respectively, for warm water quenched specimensaged at different conditions. Table 18 shows the effect of Cu, Mg andaging condition on yield strength of the Al-9Si-0.15Fe-0.55Mn—Cu—Mgalloys. After being completely solidified, the tensile bar castings werecooled in warm water. As shown in Table 18, Mg and Cu content showedsignificant impact on yield strength. Table 19 shows the effect of Cu,Mg and aging condition on ultimate tensile strength of theAl-9Si-0.15Fe-0.55Mn—Cu—Mg alloys. After being completely solidified,the tensile bar castings were cooled in warm water. Table 20 shows theeffect of Cu, Mg and aging condition on elongation of theAl-9Si-0.15Fe-0.55Mn—Cu—Mg alloys. After being completely solidified,the tensile bar castings were cooled in warm water.

Alloys with 0.4% Mg and 1.0-1.5% Cu showed higher yield strength thanother alloys. For warm water quenched specimens, the highest achievedyield strength in the T5 condition was about 260 MPa.

TABLE 18 Yield Strength for R1-R6 Alloys (Water Cool) at VariousArtificial Aging Conditions Average Tensile Yield Strength StandardDeviation 190° C./ 205° C./ 190° C./ 205° C./ Alloy 175° C./6 hrs 6 hrs6 hrs 175° C./6 hrs 6 hrs 6 hrs R1 194 201 193 2.1 2.8 4.1 R3 195 205180 16.5 10.3 7.6 R5 246 232 222 17.9 22.0 3.4 R2 227 234 232 6.2 11.77.6 R4 256 261 243 6.2 6.2 23.4 R6 239 267 251 5.5 6.9 15.8

TABLE 19 Tensile Strength for R1-R6 Alloys (Water Cool) at VariousArtificial Aging Conditions Average Ultimate Tensile Strength StandardDeviation 190° C./ 205° C./ 190° C./ 205° C./ Alloy 175° C./6 hrs 6 hrs6 hrs 175° C./6 hrs 6 hrs 6 hrs R1 285 298 274 9.0 19.3 4.8 R3 268 283235 30.3 18.6 46.9 R5 289 274 247 7.6 18.6 2.1 R2 294 278 278 11.0 28.99.6 R4 306 279 291 23.4 1.4 20.7 R6 293 293 291 23.4 4.1 17.2

TABLE 20 Elongation for R1-R6 Alloys (Water Cool) at Various ArtificialAging Conditions Average Elongation Standard Deviation 190° C./ 205° C./190° C./ 205° C./ Alloy 175° C./6 hrs 6 hrs 6 hrs 175° C./6 hrs 6 hrs 6hrs R1 2.7 3.7 3.0 0.8 1.4 0.5 R3 2.2 2.5 2.2 0.6 0.5 1.6 R5 1.7 1.3 1.30.3 0.6 0.6 R2 2.2 2.0 1.7 0.3 0.5 0.3 R4 1.7 0.8 1.5 0.6 0.3 0.0 R6 1.80.8 1.5 0.3 0.3 0.0

EXAMPLE 5 Cast Alloys for HPDC Engine Block Applications

Additional high-pressure die-casting (HPDC) tests were completed on twoalloys, the compositions of which are shown below in Table 21. Thealloys were cast as journal pieces. After casting, various ones of thealloys were quenched in air, while other ones of the alloys werequenched in warm water (≈60° C.). Various ones of the alloys were agedat various times and temperatures, after which various mechanicalproperties were tested, the results of which are provided in Tables22-24, below. Strength and elongation were tested using JIS14B testspecimens taken from about 1 mm below the casting surface.

TABLE 21 Actual Composition of Example 5 Alloys (weight percent) AlloySi Cu Mg Fe Mn Ti V Zr Sr B R7 9.15 0.52 0.19 0.16 0.57 0.10 0.13 0.110.013 0.0018 R8 9.24 1.10 0.41 0.17 0.53 0.11 0.12 0.13 0.014 0.0017 Theweight ratio of Fe:Mn for all alloys was from 0.28 to 0.32.

TABLE 22 T5 properties of Alloys Aged at about 205° C. for about 6 hours(values averages of five specimens; standard deviation shown) AlloyQuench UTS (MPa) TYS (MPa) Elong. (%) R7 Air 248.8 ± 9.2  136.9 ± 11.15.6 ± 1.3 R7 Water 278.6 ± 4.0  177.9 ± 1.2  4.4 ± 0.7 R8 Air 249.1 ±10.3 140.9 ± 15.7 3.8 ± 0.5 R8 Water 295.7 ± 4.1  210.5 ± 1.5  2.7 ± 0.2

TABLE 23 T5 properties of Alloys Aged at about 205° C. for various times(values averages of five specimens; standard deviation shown; all waterquenched) Alloy Aging Time UTS (MPa) TYS (MPa) Elong. (%) R8 2 hours298.4 ± 9.5 224.0 ± 2.2 2.2 ± 0.4 R8 4 hours 300.3 ± 4.0 220.3 ± 1.3 2.4± 0.2 R8 6 hours 295.7 ± 4.1 210.5 ± 1.5 2.7 ± 0.2

TABLE 24 T5 fatigue Properties of Alloy R8 (water quenched and aged atabout 205° C. for 6 hours) Sample Stress amplitude Number of cycles No.σ_(a) (MPa) (Nf) Condition 1 110  1.00E+06 Fracture 2 90  1.00E+07 OK 393  1.00E+07 Fracture 4 93 3.998E+06 Fracture 5 95  1.82E+06 Fracture 6120 3.596E+05 Fracture 7 110  7.37E+05 Fracture 8 100 2.206E+06 Fracture9 90  1.00E+07 OK 10 100 2.915E+06 FractureThe fatigue properties of alloy R8 were measured at room temperature, ata stress ratio of R=−1 (=σ_(min)/σ_(max)) with a frequency of 1500 rpm,and with a mean stress (σ_(m)) of zero (0) MPa. The fatigue was 90 MPaat room temperature.

Fatigue strength (staircase fatigue) at about 150° C. was also measuredfor alloy R8 in one T5 temper, having been water quenched andartificially aged for about 6 hours at about 205° C. Alloy R8 in thistype of T5 temper realized a mean fatigue strength of 81.25±7.83 MPa at150° C. The stress amplitude increment was 5.0 MPa and the convergencefactor was 0.94.

It will be understood that the embodiments described herein are merelyexemplary and that a person skilled in the art may make many variationsand modifications without departing from the spirit and scope of theclaimed subject matter. For example, use different aging conditions mayproduce different resultant characteristics. All such variations andmodifications are intended to be included within the scope of theappended claims.

What is claimed is:
 1. An aluminum casting alloy consisting of: 8.5-9.5wt. % silicon; 0.8-2.0 wt. % copper (Cu); wherein 2.5≦ (Cu+10Mg)≦5.8;0.20-0.53 wt. % magnesium (Mg); 0.35 to 0.8 wt. % manganese; up to 5.0wt. % zinc; up to 1.0 wt. % silver; up to 1.0 wt. % nickel; up to 1.0wt. % hafnium; up to 1.0 wt. % iron; up to 0.30 wt. % titanium; up to0.30 wt. % zirconium; up to 0.30 wt. % vanadium; up to 0.10 wt. % of oneor more of strontium, sodium and antimony; other elements being ≦0.04wt. % each and ≦0.12 wt. % in total; the balance being aluminum.
 2. Thealloy of claim 1, wherein the ratio of iron to manganese is ≦0.5.
 3. Thealloy of claim 2, wherein the alloy includes from 1.0 to 1.5 wt. % Cu.4. The alloy of claim 3, wherein the alloy includes from 0.4 to 0.45 wt.% Mg, and wherein 4.7≦(Cu+10Mg)≦5.8.
 5. The alloy of claim 4, whereinthe alloy includes from 0.10 to 0.30 wt. % Fe.
 6. The alloy of claim 5,wherein the alloy includes from 0.45-0.70 wt. % Mn.
 7. The alloy ofclaim 6, wherein the alloy includes of at least 0.05 wt. % V and atleast 0.05 wt. % Zr, and wherein the total amount of Zr+V is from 0.10wt. to 0.50 wt. %.
 8. A method comprising: (a) introducing the moltenaluminum alloy of claim 1 into a mold; (b) removing a defect-free shapecast article from the mold; and (c) tempering the shape cast article toone of a T5, T6 or T7 temper.
 9. The method of claim 8, wherein the moldis a high pressure die casting mold and the step of introducing is byhigh pressure die casting.